Gallic Roman invasions of Italy

The Gallic Roman invasions of Italy were a series of military campaigns undertaken by the Gallic Empire against Aurelian's faction of the Roman Empire during the Crisis of the Third Century. The Gallic Empire attempted to take advantage of Aurelian's preoccupation with subduing the pretender Quintillus' usurpation in Rome in the south by invading the undefended north of Italy, but, each time the Gallic Roman forces captured a city, the city was quickly reconquered by Aurelian's Legio I Dacica.

Background
The Crisis of the Third Century shattered the Roman Empire, which fragmented into several territorial divisions: in the east was the Palmyrene Empire of Zenobia, in Central Europe and the Balkans was Aurelian's loyalist faction of the Roman Empire, in Italy was the pretender Quintillus' faction, and in Western Europe and Britain was the Gallic Empire of Tetricus I. While Zenobia was not immediately at war with Aurelian, instead chipping away at the lands of his allied provincial leaders in Asia Minor and Egypt, Tetricus and Quintillus were instant rivals of Aurelian.

Aurelian believed that the pretenders in Rome were the most latent threat to his rule, so he decided to lead his Legio I Dacica from Zarmizegetusa in Dacia and into Italy, where he intended to confront and defeat Quintillus' loyalists. Meanwhile, the Gallic Empire was dormant, building up its legions and focusing on their own imminent threats, the invading Germanic tribes from across the Rhine.

By early 271 AD, Aurelian's armies had conquered the northern third of Italia, while other legions landed in other parts of Italy to cut up the peninsula and conquer it piecemeal. Aurelian originally intended to march on Rome himself and claim glory for himself, and his army replenished its ranks in the recently-captured port city of Genua. However, Gallic Rome had other plans, intending on taking advantage of the absence of Aurelian's legion to conquer the north and trap Aurelian's legions on the peninsula.

Campaigns
The first invasion of northern Italia was carried out by Gaul's Legio IV Victrix, commanded by Titus Oranius. This small legion of 671 men captured Mediolanium with 178 losses, and they occupied the city and raised a small and undermanned garrison under Pacuvius Trebellius Scrofa. Aurelian quickly marched north from Genoa with his legion to retake Mediolanium, and his army assaulted the city. The 1,743-strong Legio I Dacica took the city from its 976-strong garrison with 385 losses, and, with northern Italy back in his hands, Aurelian was able to issue a provincial edict once again.